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-rw-r--r--arch/arm/kernel/entry-armv.S49
1 files changed, 49 insertions, 0 deletions
diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index d9fb819bf7c..2a8d27e18fa 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -614,6 +614,47 @@ __kuser_helper_start:
/*
* Reference prototype:
*
+ * void __kernel_memory_barrier(void)
+ *
+ * Input:
+ *
+ * lr = return address
+ *
+ * Output:
+ *
+ * none
+ *
+ * Clobbered:
+ *
+ * the Z flag might be lost
+ *
+ * Definition and user space usage example:
+ *
+ * typedef void (__kernel_dmb_t)(void);
+ * #define __kernel_dmb (*(__kernel_dmb_t *)0xffff0fa0)
+ *
+ * Apply any needed memory barrier to preserve consistency with data modified
+ * manually and __kuser_cmpxchg usage.
+ *
+ * This could be used as follows:
+ *
+ * #define __kernel_dmb() \
+ * asm volatile ( "mov r0, #0xffff0fff; mov lr, pc; sub pc, r0, #95" \
+ * : : : "lr","cc" )
+ */
+
+__kuser_memory_barrier: @ 0xffff0fa0
+
+#if __LINUX_ARM_ARCH__ >= 6 && defined(CONFIG_SMP)
+ mcr p15, 0, r0, c7, c10, 5 @ dmb
+#endif
+ mov pc, lr
+
+ .align 5
+
+/*
+ * Reference prototype:
+ *
* int __kernel_cmpxchg(int oldval, int newval, int *ptr)
*
* Input:
@@ -642,6 +683,8 @@ __kuser_helper_start:
* The C flag is also set if *ptr was changed to allow for assembly
* optimization in the calling code.
*
+ * Note: this routine already includes memory barriers as needed.
+ *
* For example, a user space atomic_add implementation could look like this:
*
* #define atomic_add(ptr, val) \
@@ -698,10 +741,16 @@ __kuser_cmpxchg: @ 0xffff0fc0
#else
+#ifdef CONFIG_SMP
+ mcr p15, 0, r0, c7, c10, 5 @ dmb
+#endif
ldrex r3, [r2]
subs r3, r3, r0
strexeq r3, r1, [r2]
rsbs r0, r3, #0
+#ifdef CONFIG_SMP
+ mcr p15, 0, r0, c7, c10, 5 @ dmb
+#endif
mov pc, lr
#endif